The present document is based on Japanese Priority Document JP 2000-289444, filed in the Japanese Patent Office on Sep. 22, 2000, the entire contents of which being incorporated herein by reference.
1. Technical Field of the Invention
This invention relates to a polishing method and a polishing apparatus. More specifically, the present invention relates to the method and the apparatus for polishing a surface of a member to be processed having bumps and dips against a plane or a curved surface intended for processing by using slurry including a particle.
2. Description of the Related Art
As disclosed in Japanese Unexamined Patent Application Publication No. H11-288906, a processing method of a CMP (Chemical Mechanical Polishing) has widely been used conventionally in a flattening process of a semiconductor wafer substrate.
According to the conventional CMP processing method as shown in FIG. 1, an elastic polishing pad 12 is fixedly glued on a rotatable polishing plate 11. On the other hand, a silicon wafer 13 is fixed to an end face of a polishing head 14, and a surface to be polished of the silicon wafer 13 is made crimped to the polishing pad 12 with the bottom up. Under such condition, while slurry 15 is supplied, the polishing plate 11 and the polishing head 14 are respectively rotated, thereby the surface of the silicon wafer 13 is polished.
At this time, the slurry 15 does not flow sufficiently into a portion to be polished because the polishing pad 12 and the silicon wafer 13 are contacted each other under pressurized condition, so that a polishing condition is apt to be unstable. To prevent such unstable polishing condition, the surface of the polishing pad 12 is made dressed by a diamond tool or the like to form a comparatively large bumps and dips for providing slurry puddles. Therefore, on the surface of the polishing pad 12 made of an elastic body, there is formed a fuzzy produced due to scratches caused by the slurry puddles and the dressing tool.
The silicon wafer 13 polished by the CMP processing method as shown in FIG. 1 includes regularly arranged bumps of a wiring pattern 21 or the like on the surface layer of the silicon wafer 13 as shown in FIG. 2, and a thin film layer 22 also covers upper portion of the silicon wafer 13 as an insulation film. Accordingly plural bumps 23 are created on the surface of the thin film layer 22 with an influence of the bumps of the wiring pattern 21. According to the flattening process by the CMP processing method, the flattening process may be achieved by selectively polishing only the bumps 23 of the bumpy surface of the thin film layer 22.
Accordingly, trials have been made to polish by contacting only the bumps 23 of the silicon wafer 13 with the polishing pad 12 by increasing a coefficient of elasticity thereof. However, actually as shown in FIG. 3, the surface of the polishing pad 12 is composed of the elastic body deformed under the pressure and has the shape of fuzz having been created, so that the surface of the polishing pad 12 contacts not only with the bumps 23 but also the dips of the thin film layer 22. Namely, it is not possible to selectively polish only the bumps 23 of the thin film layer 22.
Accordingly, it has been difficult to realize an ideal flattening process to selectively remove the bumps 23 by polishing only the portions of the bumps 23 on a large scale as shown by a removed portion 24 in FIG. 4. Namely, actually as shown in FIG. 5, the removed portion 24 has roughly a constant thickness having no relation with the bumpy surface, and the bumps 23 of the thin film layer 22 formed on the surface of the silicon wafer 13 has been polished in almost uniform even with the progress of polishing, which has presented a problem that flattening is not easy to progress.
Such a phenomenon has been seen also in the case of processing an aspherical lens. Namely, a polishing process is practiced in such method that an aspherical shape obtained normally through a highly accurate grinding process is created, thereafter a damaged surface layer is removed and at the same time a surface roughness as an optical element is secured.
However, according to such polishing process, even if a polishing position and an amount of removal in that position has been calculated in accordance with the prior measurement, the peripheral portion has also been polished at the same time because the shape of removal by polishing has a certain area. In consequence, the region other than intended portion has also been polished, resulting in that accuracy of polishing achieved in the grinding process has been deteriorated on the contrary.
This invention has been made to solve such above-described problems, and to provide a polishing method and a polishing apparatus for obtaining a plane or a curved surface targeted for polishing by relatively increasing an amount of removal particularly of bumps, when polishing the surface of a member to be processed having bumpy surface.
In the polishing method for polishing the surface of the member to be processed having the bumps and dips against the plane or the curved surface targeted for processing by using a slurry including particles, a principal invention regarding the polishing method relates to the polishing method characterized in that a laser beam is irradiated to a position from which a selectively large amount of removal by polishing is desired to be acquired, thereby relatively increasing the amount of removal by polishing of that position.
Herein, by deciding a traveling route of a laser beam and a scanning position in accordance with a shape of the bumps and dips on the surface of the member, an amount of removal by polishing of the portion irradiated by the laser beam on the surface of the member may relatively be increased. It may also be accepted that a shading mask according to the shape of the bumps and dips on the surface of a member to be processed is disposed in the laser beam path to relatively increase the amount of removal by polishing of the portion irradiated by laser beam on the surface of a member to be processed which is an area exposed through the shading mask.
It may also be accepted that the particles in the slurry are made to be caught and collected on the portion irradiated by the laser beam on the surface of the member through a laser trapping phenomenon occurred by radiation pressure of a laser beam, and concentration rate of the particles in the slurry near the portion irradiated by the laser beam is made locally increased, thereby increasing the amount of removal by polishing on the surface. It may also be accepted that on the portion irradiated by the laser beam on the surface, a chemical reaction layer is made formed by a chemical reaction between the surface of the member and a slurry liquid caused by energy of the laser beam, and the chemical reaction layer is made removed by polishing by the particles in the slurry, thereby increasing the amount of removal by polishing on the surface of the member. It may also be accepted that the particles in the slurry are made to be caught and collected on the portion irradiated by the laser beam on the surface of a member to be processed through the laser trapping phenomenon occurred by the radiation pressure of the laser beam, and the concentration rate of the particles in the slurry near the portion irradiated by the laser beam is made locally increased, and moreover, on the portion irradiated by the laser beam on the surface of the member, the chemical reaction layer is made formed by the chemical reaction between the surface of the member and the slurry liquid caused by energy of the laser beam, and the chemical reaction layer is made removed by polishing with the particles in the slurry, thereby increasing the amount of removal by polishing on the surface of the member to be processed.
It may also be accepted that prior to or during polishing process, a surface shape of the portion to be polished on the surface of the member is measured and stored, and from that measurement data, a position of the laser beam irradiation, a condition of the laser beam irradiation and a condition of polishing are calculated, thereby performing the laser beam irradiation and the polishing process in accordance with a result of that calculation.
In the polishing apparatus for polishing the surface of the member having the bumps and dips against the plane or the curved surface targeted for processing by using the slurry including the particles, a principal invention regarding the polishing apparatus includes; laser optical system for projective irradiation of laser beam; and polishing tool system for providing pressure in an axial direction and rotational motion; and further, this invention relates to the polishing apparatus characterized in that the aforesaid laser optical system and the aforesaid polishing tool system execute relative motion with the surface of the member to be processed, whereby irradiation of laser beam and polishing are performed simultaneously or successively on the same position of the surface of the member to be processed.
Herein, it may be accepted that prior to or during a polishing processing, the surface shape of the portion to be polished on the surface of the member is measured by a shape measuring means, and the measured shape is stored in a storage means, and from the stored measurement data, the position of the laser beam irradiation, the condition of irradiation and the condition of polishing are calculated, and according to the result of the calculation, the aforesaid laser optical system performs the laser irradiation, and the aforesaid polishing tool system performs polishing. It may also be accepted that in the beam path of the laser optical system, the shading mask is disposed, and irradiation of the laser beam is performed selectively in accordance with the shape of the bumps and dips on the surface of a member to be processed through the shading mask.
Other features and advantages of this invention will appear more fully from the following description.